1. Field of the Invention
This invention relates to a process for the disposal of polychlorinated biphenyls. It particularly relates to a molten salt process for the pyrolytic and oxidative decomposition of PCB with negligible environmental pollution.
2. Prior Art
Polychlorinated biphenyls have high thermal stability, are substantially chemically inert and have a high dielectric constant, all of which make them desirable for use in various applications, such as fire resistant transformers and capacitors. The PCB's have been in use for decades and it is reported over a half million tons have been manufactured in the United States. Production of PCB was stopped when it was found that the substances were both toxic and suspected carcinogens. However, it has been estimated that 300 million pounds of these chemicals are in land fills and about 750 million pounds are still in use.
As a result of the toxicity and suspected carcinogenity of PCB's, the Environmental Protection Agency (EPA) has issued regulations governing their storage and the treatment required to effect their disposal. Most toxic organic chemicals are readily destroyable at temperatures of about 1000.degree. C. with a residence time of two seconds by a combination of pyrolysis and oxidation reactions. However, it has been reported that the more toxic compounds, such as polychlorinated biphenyls, are also more stable and may require higher temperatures and longer residence times. Specifically, the EPA has determined that the effective destruction of PCB's by combustion requires certain criteria, namely, maintenance of the introduced liquids at a temperature of 1200.degree. C. for a two-second dwell time and 3% oxygen in the stack gas or maintenance of the introduced liquid at a temperature of 1600.degree. C. for one and one-half seconds dwell time and 2% excess oxygen in the stack gas. In addition, the regulations applicable to PCB's also apply to PCB-contaminated mixtures. Thus, in accordance with the EPA regulations, any liquid containing as little as 500 parts per million PCB must be stored and destroyed in accordance with EPA regulations.
It will be readily apparent to those skilled in the art that the high temperatures required in accordance with EPA regulations for the destruction of PCB necessitates the use of exotic and expensive materials of construction for an incinerator. Obviously, therefore, it would be desirable to develop a lower temperature process which would still provide for the complete destruction of the PCB with negligible environmental pollution. It would be even more desirable if such process could operate with a shorter residence time without any adverse effect on the destruction of the PCB, since a reduction in residence time would make it possible to use a much smaller incinerator for any given throughput of PCB.